CHYMOSIN; PARACHYMOSIN. 451 



specially shown by FuLD, 1 within certain limits, the coagulation t, 

 multiplied by the quantity of rennin, I, equals a constant, k. As shown 

 by BANG, this law does not apply to parachymosin. 



Parachymosin differs from chymosin by being much more resistant 

 toward acids, but is more readily destroyed by alkalies. Calcium 

 chloride accelerates the casein coagulation with parachymosin very 

 much more than with chymosin. GEWIN 2 has raised objections to these 

 points of difference between chymosin and parachymosin, although the 

 proofs that he puts forth are still not so conclusive that we have 

 sufficient ground to doubt the existence of parachymosin. 



A much -discussed question is, whether the digestion of protein and 

 the rennet action are brought about by two special enzymes, or represent 

 two different enzyme actions, or whether there is only one enzyme, the 

 pepsin, which has both actions. The supporters of this last view dispose 

 of the question in different ways. Some, like PAWLOW and PARAST- 

 SCHUK, consider the rennet action simply as the reverse of the synthetical 

 action of pepsin, a view which is improbable in the highest degree. Others, 

 such as SAWJ ALOW 3 and GEWIN, consider, on the contrary, that the coagula- 

 tion of milk is only a pepsin action and indeed as the first step in the 

 beginning of proteolygis, namely the beginning of peptic digestion of 

 casein. 



The simultaneous occurrence in the animal and plant kingdoms of 

 enzymes having a proteolytic and rennet action indicates an identity 

 of both enzymes and enzyme actions and the parallelism of the pepsin 

 and rennet action. This parallelism in fact does not prove much, because 

 it has mostly been studied in acid reaction, while rennet is character- 

 istically active in neutral or faintly alkaline reaction. 



The pathological cases in man, if the observations are reliable, where 

 only one enzyme action occurs, seems to suggest the identity of the 

 action of both enzymes. In opposition, however, is the fact that pepsin, 

 so far as known, only has a digestive action in the presence of free H ions, 

 while the coagulation of milk occurs in the absence of these and indeed 

 in the presence of HO ions. Among other facts which contravene the 

 identity is the fact that a pepsin solution can be prepared which has a 

 digestive action but cannot coagulate milk, and the reverse, namely, 

 rennet solutions can be made which coagulate milk but do not have 

 digestive action in acid reaction (H AMMARSTEN) . The observations of 



1 Hofmeister's Beitrage 2; Bang, 1. c. 



2 Zeitschr. f. physiol. Chem., 54. 



3 The recent literature on this question can be found in Hammarsten, Zeitschr. 

 f. physiol. Chem., 56. 



